1,660 research outputs found
Lattice QCD with mixed actions
We discuss some of the implications of simulating QCD when the action used
for the sea quarks is different from that used for the valence quarks. We
present exploratory results for the hadron mass spectrum and pseudoscalar meson
decay constants using improved staggered sea quarks and HYP-smeared overlap
valence quarks. We propose a method for matching the valence quark mass to the
sea quark mass and demonstrate it on UKQCD clover data in the simpler case
where the sea and valence actions are the same.Comment: 15 pages, 10 figures some minor modification to text and figures.
Accepted for publicatio
Pakistan Panel Household Survey: Sample Size and Attrition
The socio-economic databases in Pakistan, as in most
countries, can be classified into three broad categories, namely
registration-based statistics, data produced by different population
censuses and household survey-based data. The registration system of
births and deaths in Pakistan has historically been inadequate [Afzal
and Ahmed (1974)] and the population censuses have not been carried out
regularly. The household surveys such as Pakistan Demographic Survey
(PDS), Labour Force Survey (LFS) and Household Income Expenditure Survey
(HIES) have been periodically conducted since the 1960s. These surveys
have filled the data gaps created by the weak registration system and
the irregularity in conducting censuses. The data generated by the
household surveys have also enabled social scientists to examine a wide
range of issues, including natural increase in population, education,
employment, poverty, health, nutrition, and housing. All these surveys
are, however, cross-sectional in nature so it is not possible to gauge
the dynamics of these social and economic processes, for example the
transition from school to labour market, movement into or out of
poverty, movement of labour from one state of employment to another. A
proper understanding of such dynamics requires longitudinal or panel
datasets where the same households are visited over time. Since panel
surveys are complex and expensive to carry out, they are not as commonly
conducted as the cross-sectional surveys anywhere in the world and in
Pakistan they are even rare
Welfare Impact of the Lady Health Workers Programme in Pakistan
With the year 2015 fast approaching, Pakistan is not likely to
achieve most of the health targets set in the Millennium Development
Goals [Pakistan (2010)]. High levels of child and maternal mortality and
child malnutrition are among the major health challenges facing the
country. Along with this enhanced vulnerability for children and women
there is also an economic divide in the society because these health
challenges are more profound for the poor segment of the population than
for the better off. Another divide is between the rural and urban
populations due to concentration of health facilities in urban centres
of the country. The high cost of dealing with health issues adversely
affects the poor and rural population, lowering their productivity and
limiting their lifetime achievements. Without substantially improved
health outcomes it is impossible to break out of the cycle of poverty
[OECD (2003)]
A 0-dimensional counter-example to rooting?
We provide an example of a 0-dimensional field theory where rooting does not
work.Comment: 3 pages; Physics Letters B (2010
The ratio m_c/m_s with Wilson fermions
We determine the quark mass ratio m_c/m_s on the lattice, using Wilson-type
fermions. Configurations with N_f=2 dynamical clover-improved fermions by the
QCDSF collaboration are used, which were made available through the ILDG. In
the valence sector we use a sophisticated, mass-independently O(a)-improved
Wilson-type action with small cut-off effects even in the charm mass region.
After an extrapolation to the physical pion mass, to zero lattice spacing and
to infinite box volume, we find m_c/m_s=11.27(30)(26).Comment: 7 pages, 1 figure; v2: more statistics, improved analysis and
presentation, 1 reference adde
High-precision determination of the light-quark masses from realistic lattice QCD
Three-flavor lattice QCD simulations and two-loop perturbation theory are
used to make the most precise determination to date of the strange-, up-, and
down-quark masses, , , and , respectively. Perturbative matching
is required in order to connect the lattice-regularized bare- quark masses to
the masses as defined in the \msbar scheme, and this is done here for the first
time at next-to-next-to leading (or two-loop) order. The bare-quark masses
required as input come from simulations by the MILC collaboration of a
highly-efficient formalism (using so-called ``staggered'' quarks), with three
flavors of light quarks in the Dirac sea; these simulations were previously
analyzed in a joint study by the HPQCD and MILC collaborations, using
degenerate and quarks, with masses as low as , and two values of
the lattice spacing, with chiral extrapolation/interpolation to the physical
masses. With the new perturbation theory presented here, the resulting \msbar\
masses are m^\msbar_s(2 {GeV}) = 87(0)(4)(4)(0) MeV, and \hat m^\msbar(2
{GeV}) = 3.2(0)(2)(2)(0) MeV, where \hat m = \sfrac12 (m_u + m_d) is the
average of the and masses. The respective uncertainties are from
statistics, simulation systematics, perturbation theory, and
electromagnetic/isospin effects. The perturbative errors are about a factor of
two smaller than in an earlier study using only one-loop perturbation theory.
Using a recent determination of the ratio due to
the MILC collaboration, these results also imply m^\msbar_u(2 {GeV}) =
1.9(0)(1)(1)(2) MeV and m^\msbar_d(2 {GeV}) = 4.4(0)(2)(2)(2) MeV. A
technique for estimating the next order in the perturbative expansion is also
presented, which uses input from simulations at more than one lattice spacing
Ginsparg-Wilson Pions Scattering in a Sea of Staggered Quarks
We calculate isospin 2 pion-pion scattering in chiral perturbation theory for
a partially quenched, mixed action theory with Ginsparg-Wilson valence quarks
and staggered sea quarks. We point out that for some scattering channels, the
power-law volume dependence of two pion states in nonunitary theories such as
partially quenched or mixed action QCD is identical to that of QCD. Thus one
can extract infinite volume scattering parameters from mixed action
simulations. We then determine the scattering length for both 2 and 2+1 sea
quarks in the isospin limit. The scattering length, when expressed in terms of
the pion mass and the decay constant measured on the lattice, has no
contributions from mixed valence-sea mesons, thus it does not depend upon the
parameter, C_Mix, that appears in the chiral Lagrangian of the mixed theory. In
addition, the contributions which nominally arise from operators appearing in
the mixed action O(a^2 m_q) Lagrangian exactly cancel when the scattering
length is written in this form. This is in contrast to the scattering length
expressed in terms of the bare parameters of the chiral Lagrangian, which
explicitly exhibits all the sicknesses and lattice spacing dependence allowed
by a partially quenched mixed action theory. These results hold for both 2 and
2+1 flavors of sea quarks.Comment: 27 pages, 3 figures. Mistakes corrected in Eqs. (37), (42). Improved
discussion in section 4 and related results in Eqs. (33), (37), (40) and
(42). Added references. Version to be published in PR
Two-Pion Exchange in Proton-Proton Scattering
The contribution of the box and crossed two-pion-exchange diagrams to
proton-proton scattering at 90 is calculated in the laboratory
momentum range up to 12 GeV/c. Relativistic form factors related to the nucleon
and pion size and representing the pion source distribution based on the quark
structure of the hadronic core are included at each vertex of the pion-nucleon
interaction. These form factors depend on the four-momenta of the exchanged
pions and scattering nucleons. Feynman-diagram amplitudes calculated without
form factors are checked against those derived from dispersion relations. In
this comparison, one notices that a very short-range part of the crossed
diagram, neglected in dispersion-relation calculations of the two-pion-exchange
nucleon-nucleon potential, gives a sizable contribution. In the Feynman-diagram
calculation with form factors the agreement with measured spin-separated cross
sections, as well as amplitudes in the lower part of the energy range
considered, is much better for pion-nucleon pseudo-vector vis \`a vis
pseudo-scalar coupling. While strengths of the box and crossed diagrams are
comparable for laboratory momenta below 2 GeV/c, the crossed diagram dominates
for larger momenta, largely due to the kinematics of the crossed diagram
allowing a smaller momentum transfer in the nucleon center of mass. An
important contribution arises from the principal-value part of the integrals
which is non-zero when form factors are included. It seems that the importance
of the exchange of color singlets may extend higher in energy than expected
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